Method of resin sealing semiconductor devices

ABSTRACT

A method of resin sealing semiconductor devices wherein semiconductor devices, such as semiconductor chips, are placed in cavities provided in a pair of chase blocks which are clamped by a press machine through support members capable of elastic compressive deformation. Plastic is then injected into the cavities of the chase blocks to resin seal the semiconductor devices.

This application is a division of application Ser. No. 219,483, filedJuly 15, 1988, now U.S. Pat. No. 4,915,608.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an improvement in a method of and a device forresin sealing semiconductor devices.

2. Description of the Prior Art

FIG. 1 shows a conventional device for resin sealing semiconductor chipsattached to a lead frame. This device is disclosed in Japanese PublishedPatent Application 26827/87. As shown in the drawing, a chase block 1 isequipped with a plurality of cavities (not shown) accommodatingsemiconductor devices (not shown) mounted on lead frames. This chaseblock 1 is of the same height as a chamber block (not shown) equippedwith a well-known potting section (not shown) for injecting plastic aswell as a runner section (not shown). The chamber block and chase block1 are fastened to a retention board 2 by means of bolts. Heaters 3 forheating the chamber block (not shown) and chase block 1 and keeping themwarm are inserted into retention board 2. Spacer blocks 4 supporting theretention board 2 on the base 7 are provided with guide grooves 4a forfixtures 8 for fixing the entire device mentioned above to a well-knownpress slide frame 9. A post 6 supports the retention board 2 on the base7. Posts 5 on both sides of the post 6 also support the retention board2. The post 6 is higher than the posts 5, which are higher than thespacer blocks 4. These differences in height are shown as δ₁, δ₂ in FIG.2. In regard to the retention board 2 which serves as a continuous beamand the spacer blocks and the posts 5, 6 as fulcrums, the differencesδ₁, δ₂ may be determined by calculating the height of the posts 5 and 6from the reaction force and spring constant at each fulcrum (i.e. at thespacer blocks 4 and the posts 5, 6) under the press clamping force. Thecondition for this calculation is that the height of the spacer blocks 4and the posts 5, 6 under the press clamping force be the same. The base7, which supports retention board 2 through the spacer blocks 4 andposts 5, 6, contains an insulating plate 7a for preventing the heat ofthe heaters 3 from being transmitted to the press slide frame 9. Thechase block 1, chamber block, retention board 2, spacer blocks 4, posts5, 6 and base 7 form a lower die. An upper die 10 of the resin sealingdevice has substantially the same construction as the lower diedescribed above. Reference numeral 11 denotes a press platen and 12 aparting surface of said chase block 1.

In a device thus constructed, the press clamping force during a resinsealing operation causes a uniform load to be applied to the partingsurface 12. This load is received by the retention board 2, and is thendistributed to the posts 5 and 6. The load thus distributed is thenreceived by the base 7 and finally received by the press slide frame 9.Since the height of the posts 5 and 6 are so determined that the upperends of the spacer blocks 4 and the posts 5, 6 are in one plane afterthe deflection caused by the press clamping force, the parting surface12 of the chase block 1 can be, as shown in FIG. 3, kept planar. Theposts 5, 6 and the spacer blocks 4 are formed beforehand with dimensionsbased on the calculation formula. Then, after assembling the device, theheight of the posts 5, 6 and the spacer blocks 4 are adjusted by gaugingwhile checking how the die faces meet each other. As stated above, theheaters 3 inserted into the retention board 2 heat the chase block 1 andkeep it warm. Transmission and radiation of the heat generated in theprocess to the base 7 through the retention board 2, the posts 5, 6 andthe spacer blocks 4 is prevented by the insulating plate 7a provided inthe base 7. In other words, the insulating plate 7a prevents the heattransmission to the base 7 and thence to the press slide frame 9 thatwould otherwise take place through the posts 5, 6 and the spacer blocks4 which are attached to both the retention board 2 and the base 7. Theexperimental temperature is 180° C. on the parting surface 12 and 120°C. on the surface of the base 7 on the side of the retention board 2.The temperature on the opposite surface of the base 7, on the otherhand, is 50° C. because of the presence of the insulating plate 7a. Inthis way, the insulating plate 7a prevents the heat on the partingsurface 12 from escaping.

As described above, conventional devices for resin sealing semiconductordevices absolutely need a heat insulating plate because the heat in theretention board 2 tends to be transmitted to the base through the posts5, 6 and the spacer blocks 4. As a result, such conventional devices arerather expensive. Further, the uneven deformation of the insulatingplate that occurs over time may give rise to a clearance between theparting surfaces of the two opposing chase blocks; consequently, leadframes become subject to the generation of resin burrs.

Moreover, the height of the posts and the spacer blocks must be adjustedby gauging while checking how the die parting surfaces meet each otherduring operation, resulting in a complicated assembly process.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of this invention to provide amethod of and a device for resin sealing semiconductor devices thatprevents resin burr generation and provides an easy assembly processduring manufacture of such devices.

The method of resin sealing semiconductor devices of this inventioncomprises the steps of:

placing semiconductor devices in cavities provided in a pair of chaseblocks;

press clamping said pair of chase blocks by applying pressurizing forcesto them through respective support members capable of elasticcompressive deformation; and

injecting plastic into said cavities under this pressurized conditionsuch as to resin seal said semiconductor devices.

The device for resin sealing semiconductor devices of this inventioncomprises:

a pair of chase blocks equipped with cavities for holding semiconductordevices;

a press machine for pressing said pair of chase blocks against eachother through a pair of press surfaces;

a plurality of support members for holding said chase blocks above saidpress surfaces of the press machine and for elastically deforming duringthe press operation of said press machine; and

a plastic injection means for injecting plastic into the cavities ofsaid chase blocks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a conventional resin sealing device;

FIG. 2 is a partial section of the device of FIG. 1;

FIG. 3 shows a deflection curve during pressing in a conventionaldevice;

FIGS. 4A, 4B, and 4C are a plan view, a front view and a side view,respectively, of a first embodiment of the invention;

FIG. 5 is a side view illustrating deflection in the press section ofthe first embodiment;

FIGS. 6 to 8 illustrate modifications of the first embodiment;

FIG. 9 is a sectional view of a second embodiment of the invention;

FIG. 10 is a plan view showing the chase block in the second embodiment;and

FIG. 11 is a sectional view showing a modification of the secondembodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the invention will now be explained referring toFIGS. 4A to 4C. Illustrated in the drawings are chase blocks 20 eachequipped with a runner 20a, a plurality of cavities 20b and gates 20cconnecting the cavities 20b with the runner 20a; a chamber block 21equipped with a pot 21a and runners 21b; guide pins 22 for effectingvertical alignment; an ejector mechanism 23 for discharging productsafter resin sealing; lead frames 24 with semiconductor chips bonded tothem (shown in broken lines); first posts 25 arranged in the vicinity ofthe cavities 20b; and second posts 26 arranged under the chamber block21. As shown in FIG. 4C, the first posts 25 are longer than the secondposts 26 by a length B and longer than the spacer blocks 4 by a length A(A is greater than B). Further, the connection between the retentionboard 2 and the spacer blocks 4 is of a floating type, i.e., theretention board 2 is suspended with respect to the spacer blocks 4,raising of the retention board 2 being prevented by part (not shown) ofthe spacer blocks 4.

As shown in FIG. 5, the first posts 25 undergo elastic compressivedeformation by δ₁ or δ₂ under the press clamping forces applied to theretention board 2. The second posts 26 also undergo elastic compressivedeformation by a predetermined amount under the pressure of a plunger(not shown) when it moves inside the pot 21a. Both the first and secondposts 25 and 26 are so designed that they are higher than the spacerblocks 4 after the elastic compressive deformation. In other words, thespacer blocks 4 are always separated from the retention board 2 duringboth the pressing and the plastic injection procedure. Explanation ofthe other components will be omitted here since they are the same asthose in conventional devices.

While FIGS. 4A to 4C only illustrate the lower die, the device alsoincludes an upper die which has substantially the same construction asthe lower die, the parting surfaces of both dies being opposed to eachother.

The operation of the device will now be explained. First, the upper andlower dies are mounted on a press and closed. Then, the plastic in thepot 21a is pressed by the plunger (not shown). This plastic, which isinitially in the pot 21a of the chamber block 21, flows through therunners 20a of the chase blocks 20 and enters the cavities 20b to resinseal semiconductor chips previously set therein. These semiconductorchips are set in the cavities 20b, bonded to the lead frames 24, andprovided with gold wiring.

When pressurizing force is applied by means of a press, the first posts25 which are arranged at equal intervals in the vicinity of the cavities20b first receive the force and evenly pressurize the portions aroundthe cavities 20b through the retention board 2. In this condition, theretention board 2 has undergone parallel displacement toward the base 7by a distance corresponding to the amount of the compressivedeformation. The parting surfaces 12 of the upper and lower dies arekept in an evenly pressurized condition. When, as in FIG. 5, the presssection is bent by deformation, the compressive deformation amounts.sup.δ 1, .sup.δ 2 of the first posts 25 may be determined as severaltimes the amount of deformation A₁ of the press member during pressing.Therefore, any deformation of the press member will be easily absorbedby the elastic compressive deformation of the plurality of posts 25,whereby a uniform pressurizing force can be applied to the partingsurfaces 12. In other words, it is not necessary to check how theparting surfaces 12 of the dies meet each other before determining theheight of the first posts 25, which simplifies the work of assemblingthe device. The distance B in regard to the second post 26 should besuch that the chase blocks 20 are supported without being deformed bythe plastic injection pressure, and the distance A should be such thatthe spacer blocks 4 do not come into contact with the retention board 2even during pressing.

By supporting the retention board 2 in this way by means of the posts25, 26 which are in contact with it over a small area only, a sufficientdegree of thermal insulation can be attained. An experiment has shownthat when the temperature of the parting surface 12 is 180° C., that ofthe base 7 is 60° C., a temperature that can in practice be ignored. InTable 1, the insulation obtained by the present invention is comparedwith that of a prior art device. This table shows that the upper surfaceof the base 7 can be reduced to 60° C. because of the posts 25, 26,whereas it is as high as 120° C. in the prior art. One may conclude fromthis that the posts 25, 26 provide a sufficient thermal insulatingeffect.

                  TABLE 1                                                         ______________________________________                                                Temperature                                                                                       Lower section                                                                 of base 7                                                                     (Lower section                                            Parting  Upper section                                                                            of insulating                                             surface 12                                                                             of base 7  plate)                                            ______________________________________                                        Prior art 180° C.                                                                           120° C.                                                                           50° C.                                 This invention                                                                          180° C.                                                                            60° C.                                                                           --                                            ______________________________________                                    

While the cross-section of the first post 25 is round in the firstembodiment described above, a similar effect can be obtained byemploying posts with a rectangular cross-section and arranging themsuitably. This is shown in FIG. 6 as a second embodiment. Here, suchrectangular posts, which are longer than the posts 26 and the spacerblocks 4, are arranged between the cavities 20b.

Further, while in the above embodiment the posts 25, 26 are arrangedbetween the retention board 2 and the base 7, a similar effect can alsobe attained by arranging the posts between the blocks 20, 21 and theretention board 2 and directly pressurizing the blocks 20, 21 with thoseposts.

As will be appreciated from the above explanation of the first andsecond embodiments, the present invention provides sufficient thermalinsulation between the retention board and the base, so that theexpensive insulating plate can be dispensed over and generation withtime of resin burrs on the lead frames can be avoided for a long periodof time. Further, since the deformation during pressing is absorbed bythe elastic compressive deformation of the posts, the height of theposts can be determined beforehand, without checking how the partingsurfaces meet each other, so that the work of assembling the device canbe simplified. In particular, by making the posts in the vicinity of thecavities higher than the others, reliable closing of the cavity sectionis assured by these posts, which enhances the effect of guarding againstresin burr generation.

As shown in FIG. 7, a post 71 with a honeycomb construction can also beused. The entire post 71 may be formed from a stainless steel. Thisenhances the thermal resistance of the posts themselves, whereby thethermal transmission between the retention board 2 and the base 7 can begreatly restrained.

Further, a post 81 shown in FIG. 8 may also be used. This post 81 iscomposed of an axially elongated section 121A and flange sections 121bformed on both ends of the base section 121A for abutting againstretention board 2 and base 7. The entire post 81 may be formed from asuper strength steel. Here, the outer diameter of the base section 121Ais smaller than that of the regular posts 5, 6 and the outer diameter ofthe flange sections 121B is larger than that of the regular posts 5, 6.

This configuration enhances the thermal resistance of the poststhemselves, thereby greatly restraining the heat transmission betweenthe retention board 2 and the base 7.

Furthermore, this modification shown in FIG. 8 makes it possible to keepthe bearing stress on the flange sections 121B of the post 81 low andthe stress on the base section 121A high, so that the elasticcompressive deformation of the post can be augmented.

FIG. 9 is a sectional view of the lower die in the second embodiment ofthe device for resin sealing semiconductor chips in accordance with thepresent invention, and FIG. 10 is a plan view of the chase block in thesame embodiment. In this embodiment, a retention board 201 with built-inheaters (not shown) is fixed to a base 203 through spacer blocks 204.Cylindrical support pins 221, provided with high hardness by way of aheat treatment, are arranged below cavities (described later). Thesesupport pins 221 are all of the same height and capable of elastic axialdeformation within a permissible range of 30 to 80 μm. Chase blocks 222with a U-shaped cross section, supported by the support pins 221, arearranged on retention board 201 spaced apart from each other by apredetermined distance. The height of the side wall sections 222a ofthese chase blocks 222 is smaller than that of said support pins 221 bya distance H. The chase blocks 222 are provided with a plurality ofcavities 223 which open into parting surfaces 222b. An ejector mechanismcomposed of ejector pins 224a and ejector plates 224b is provided insideeach of the chase blocks 222. Further, the distance between the chaseblocks 222 and the retention board 201 is maintained even when thesupport pins have undergone elastic compressive deformation. Another die(not shown) of the same construction is arranged above this one.

In the device for resin sealing semiconductor devices thus constructed,the chase blocks 222 are supported by a multitude of support pins 221situated on the retention board 201 and below the cavities 223. Sincethe chase blocks 222 of the upper and lower dies (only the lower one isshown) are thus positioned apart from the retention board 201, theirdeformation during closing can be avoided by allowing only the supportpins 221 to undergo elastic compressive deformation in the axialdirection.

Accordingly, the parting surfaces 222b of the chase blocks 222 can be inclose contact with each other during closing, whereby the pressurizingforce is evenly applied to the parting surfaces 222b.

While in the second embodiment the chase blocks 222 are separated fromthe retention board 201, it is also possible, as shown in FIG. 11, toposition the spacer blocks 204 apart from the retention board 201. Thisarrangement makes it possible to prevent deformation not only of thechase blocks 225 but also of the retention block 201. In this embodimentshown in FIG. 11, support pins 226, capable of elastic compressionduring closing, support the retention board 201 above the base 203. Thisembodiment further includes heaters 227, cavities 228 and support pins229 which are similar to the support pins 221 of the second embodiment.

While the support pins 221 in the second embodiment are cylindrical,pins of different configuration, for example prism-like pins, may alsobe employed.

The number of support pins 221 is not restricted to that adopted in theabove embodiments.

As described above, the chase blocks in the embodiments shown in FIGS. 9to 11 are equipped with cavities that open into the parting surfaces.These chase blocks are supported by a multitude of support pins and arearranged on the retention board spaced apart from each other by apredetermined distance. Since these support pins are situated below thecavities, deformation of the chase blocks during closing can be avoidedand the parting surfaces can be brought into close contact with eachother. Accordingly, pressurizing force during closing can be uniformlyapplied to the parting surfaces, whereby generation of resin burrs onthe lead frames on the chase blocks can be positively prevented.

What is claimed is:
 1. A method of resin sealing semiconductor devicescomprising:placing semiconductor devices in cavities provided in a pairof chase blocks; clamping the pair of chase blocks together in a presshaving two opposed press surfaces, two bases, one of the bases beingdisposed on each of the press surfaces, two retention boards, eachretention board supporting one of the chase blocks, spacer blocksdisposed between the respective bases and retention boards, a pluralityof support members disposed between and contacting the respective basesand retention boards for transmitting forces to the chase blocks fromthe press, the support members being longer between the respective basesand retention boards than the spacer blocks; actuating the press andthereby applying a compressive force to urge the chase blocks together,the compressive force being transmitted from the press to the chaseblocks through the support members, elastically compressing the supportmembers, while maintaining clearance between the respective retentionboards and spacer blocks; and injection plastic into the cavities whileclamping the pair of chase blocks together to resin seal saidsemiconductor devices.
 2. A method of resin sealing semiconductordevices comprising:placing semiconductor devices in cavities provided ina pair of chase blocks; clamping the pair of chase blocks together in apress having two opposed press surfaces, two bases, one of the basesbeing disposed on each of the press surfaces, two retention boards, eachretention board being fixedly mounted to one of the bases, spacer blocksdisposed between the respective bases and retention boards forsupporting the retention boards, a plurality of support pins disposedbetween and contacting the respective bases and retention boards andchase blocks for transmitting forces to the chase blocks from the press,the chase blocks having recesses facing the respective retention boards,the support pins being disposed within the recesses in the chase blocksand having lengths between the respective retention boards and chaseblocks sufficient to maintain a separation between the respectiveretention boards and the chase blocks when the chase blocks are clampedtogether in the press; actuating the press and thereby applying acompressive force to urge the chase blocks together, the compressiveforce being transmitted from the press to the chase blocks through thesupport pins, elastically compressing the support pins while maintainingclearance between the respective retention boards and chase blocks; andinjecting plastic into the cavities while clamping the pair of chaseblocks together to resin seal said semiconductor devices.